A several type of cooking utensil is known and used in a kitchen and the like.
For example, the cooking utensil is made of clay, cast iron, tin or stainless steel. Then the prior cooking utensil having one layer in bottom and side wall is concentrately heated in a portion directly contacted with the flame of a burner and the like so that the cooking food in the cooking utensil is partially burned. The burned food is not good for health of human body. And in a prior frying pan, a lot of edible oil is required not to burn the cooking food.
In order to solve the above problems, as described in U.S. Pat. No. 4,204,607, a cooking utensil 100 having multi-layer in the bottom 1()1 is provided as shown in FIG. 10. The bottom 101 of the cooking utensil 100 comprises of a aluminum or copper layer 102 welded to undersurface of the bottom 101 and a stainless steel layer 103 welded to undersurface of the aluminum or copper layer 102.
The cooking utensil 100 having triply layers 101, 102, 103 in the bottom uses the high thermal conductivity of aluminum or copper. That is, the aluminum or copper layer 102 can spread the heat energy outside of the cooking utensil 100 so that heat distribution is uniformly accomplished throughout the bottom 101 of the cooking utensil 100.
The cooking utensil 100 having triply bottom layers 101, 102, 103, however, also can not solve the burning of the cooking food, because the heat from the flame is directly transmitted to the bottom 101 of the cooking utensil 100 having the aluminum or copper layer 102 and the stainless layer 103 directly contacted each other.
Particularly, the burning of the cooking food is seriously occured in the boundary portion between the triply-layer bottom and the side wall having one layer.
Another way to solve the said problem is provided, i.e. materials such as cobalt and aluminum that thermal conductivity is high is used to form the inner member of the cooking utensile or coated on the inner member.
In case of the inner member of the cooking utensile being made of aluminum, since the heat transmission speed is high, the heat transmitted from the undersurface of the bottom of the cooking utensile during cooking with heating means can speedly spread throughout the whole bottom.
Therefore, the food burning problem can be reduced to a certain extent. Some of the food cooked in the cooking utensile get scorched and sticks on the surface of the bottom of the cooking utensile, so the food burning problem can not completely solved with the inner member made of aluminum.
Furthermore, the materials such as cobalt and aluminum are tender so that the inner member can be easily scratched when uses the cooking utensil and cleans it with a scrubber.
In order to solve the prior problem, a cooking utensile having a space between double bottom layers was provided by the inventor of the present invention and published with Korean Utilitymodel Publication No. 93-1765. The prior cooking utensil 200 has, as shown in FIG. 2, a space 201 between a upper bottom layer 202 and a lower bottom layer 203. The lower bottom layer 203 is engaged with the upper bottom layer 202 at the lower portion of the side wall 204 of the cooking utensil 200.
Then, the cooking utensil 200 also has some drawbacks as follows:
1. Since the lower bottom layer 203 is engaged with the upper bottom layer 202 at the lower portion of the side wall 204 so as to prevent the lower bottom layer 203 from disengaging with the upper bottom layer 202, the cooking food in the utensil is scorched or burned at the circumferential boundary line between one layer wall 204a and double layer wall 204b of the side wall 204.
2. Controlling expansion of the heated air in the space 201 is accomplished through an aperture 205 formed in the rim of the lower bottom layer 204. Since the aperture 205 is normally opened, air in the space 201 is continously exhausted through the aperture 205 during heating the utensil. Therefore, the heated air can not fully store energy above a certain extent.